Hi
There have been plans to add rankings to Hackage and a GSOC looked
into adding them.
Roel van Dijk built reverse dependencies for Hackage which illustrated
the most popular libraries, unfortunately the link seems broken:
http://bifunctor.homelinux.net/~roel/hackage/packages/hackage.html
Of course, the best library for "you" is the one that does more of
want you need in a way that you like the most. Social proof might not
always help for this...
Best regards
Stephen